Ch. 1 - Fossil Fuel Products

Question 1

Outline the steps in the production of LDPE

Answer 1

• LDPE is produced using the high pressure method
  
  • 1000 - 3000 atm
  • 300ºC

1. Initiation
   
   • An initiator molecule such as an organic peroxide decomposes (by heat or laser light) to form peroxide free radicals
2. Activation
   
   • Occurs as the peroxide free radicals react with and open out the ethylene C=C double bond to form an activated monomer free radical
3. Propogation
   
   • Radical from Activation further attacks double bond in another ethylene molecule, resulting in the ‘addition’ of another –CH2CH2- group
   • These reactions are referred to as chain propagating reactions
   • The end of the chain with the radical eventually curls back and removes a hydrogen atom from a carbon in the middle of chain
   • The radical is now in the middle of the chain from where a branch will grow
4. Termination
   
   • Occurs when two free radical polymers react to form a covalent bond
   • This type of reaction is called a chain terminating reaction

Question 2

Structure of LDPE

Answer 2

• Branched chains as in addition reaction, end of the chain with the radical eventually curls back and removes a hydrogen atom from a carbon in the middle of chain
• No tight packing of chains, thus less extensive dispersion forces between chains
• Few crystalline regions

Question 3

• Properties of LDPE

Answer 3

Soft due to much branching of chains
Transparent due to presence of many amorphous regions
Low melting point due to the weaker dispersion forces between chains as a result of them not being tightly packed together/linear
Permeable to oxygen

Question 4

• Uses of LDPE

Answer 4

• Cling wrap
• Food packaging
• Disposable shopping bags

Question 5

Structure of HDPE

Answer 5

• Linear, unbranched chains
• Tight packing leading to extensive dispersion forces forming between chains
• Mostly crystalline - 80-95%

Question 6

Properties of HDPE

Answer 6

• Tough, strong, and rigid
• Chemically unreactive
• High tensile strength

Question 7

Uses of HDPE

Answer 7

• Playground equipment
• Kitchen utensils
• Rubbish bins

Question 8

Structure of Polyvinylchloride or PVC

Answer 8

• Large, bulky chlorine atoms along the chain (attached to every second carbon) increase stiffness
• Polar C-Cl bonds produce strong intermolecular forces

Question 9

Properties of PVC

Answer 9

• Pure PVC is near useless as C-Cl bonds make it vulnerable to UV light
• Hard inflexible polymer: Cl functional group produces chain stiffening while C-Cl polar bonds produces strong intermolecular forces
• With addition of non-volatile plasticisers, it becomes more flexible and thermal stability is also improved

Question 10

Uses of PVC

Answer 10

• Rigid forms: building industry – external cladding, guttering pipes, floor tiles
• Flexible forms: upholstery coverings for cars, electrical insulation, garden hoses
• Also used for containers as it is impervious to oils and most organic material